Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session M3: Multiphase Flows: Confined Flows |
Hide Abstracts |
Chair: Vladimir Ajaev, Southern Methodist University Room: 23B |
Tuesday, November 20, 2012 8:00AM - 8:13AM |
M3.00001: Pressure drop and void fraction during flow boiling in minichannels at different gravity levels Vladimir Ajaev, David Brutin, Lounes Tadrist We use mathematical models of two-phase flow to explain recent experimental data on flow boiling in minichannels under the conditions of hypergravity, normal gravity, and microgravity. The experimental data was obtained during parabolic flights and includes simultaneous measurements of void fraction, pressure drop, and heat transfer coefficient. At higher flow rates, void fraction grows linearly along the channel but with different slopes depending on gravity level. Using the models of motion of confined bubbles, we predict the ratio of the slopes of the void fraction profiles which is in excellent agreement with the experimental measurements. At lower flow rates, the void fraction profiles are concave down and eventually flatten away from the channel entrance. This change in the dynamics is explained by a combination of thermal effects in bubble growth, geometric confinement, and bubble coalescense. The relationship between pressure drop measurement results and flow structure is discussed. Finally, experimentally observed heat transfer enhancement under the conditions of microgravity is explained. [Preview Abstract] |
Tuesday, November 20, 2012 8:13AM - 8:26AM |
M3.00002: A mathematically-consistent formulation for evaporation of menisci in microchannels Reza Monazami, Hossein Haj-Hariri The problem of evaporation from an extended meniscus enclosed in a rectangular microchannel is investigated. A numerical model is developed to study the effect of channel width, wall superheat, as well as the working fluid. The system of differential equations describing fluid flow, heat transfer and thermodynamics can be reduced to a 4th-order ODE for the thickness of the film from its non-evaporating portion to the base of the meniscus. Prior investigations have used ad-hoc boundary conditions--such as doubling of the thickness--in order to kick start evaporation at some arbitrary point of the non-evaporating film. Such approaches result in severe underprediction of evaporative fluxes. In this talk we present a self-consistent mathematical formulation for the boundary conditions, thereby removing all arbitrariness from the solution process. The results for several channel widths and superheats as well different working fluids indicate that evaporative heat fluxes as high as 10MW/m$^2$ can be achieved. The results are validated using experiments. [Preview Abstract] |
Tuesday, November 20, 2012 8:26AM - 8:39AM |
M3.00003: On the stability of two-layer channel flow Ahmed Kaffel The effects of the viscosity, density and surface tension on the hydrodynamic instability of a two-layer viscous stratified shear flows are investigated through a linear stability analysis. In a first stage, we consider the case of isothermal, non-adiabatic, parallel two phase flows. The system of equations for stability are derived and solved numerically using the Chebyshev collocation spectral method. This algorithm is computationally efficient and accurate in reproducing the eigenvalues. The derivation of the asymptotics of these modes shows that our numerical eigenvalues are in agreement with the analytic formula obtained by Yih (1967), Kao and Park (1972), Stergios et al (1988), Pritchard et al (1992) and Pelekasis and Tsamopoulos (2001). These numerical stability results will be used for hydrodynamic problems as a tool to validate the direct numerical solver that solves the coupled two-phase liquid vapor flow dynamics with phase change to characterize the physical mechanisms underlying the quality-heat transfer relationship and thus facilitate the design of microgap channel coolers for specific two-phase heat transfer applications. [Preview Abstract] |
Tuesday, November 20, 2012 8:39AM - 8:52AM |
M3.00004: Experimental Investigation of Fluid and Particle Motion in Shear-Induced Scour Zhongfeng An, Paul Krueger A submerged particle bed subjected to fluid shear exhibits particle motion (scour) induced by drag and lift forces from the fluid at sufficiently high shear rates. To investigate this behavior, a particle bed was subjected to fluid shear in a narrow rectangular channel. The flow was driven by a pump for channel Reynolds numbers in the range 3500 -- 6000. The particle bed consisted of monodisperse borosilicate glass spheres at several initial particle bed heights. The velocity field of the continuous phase was measured using digital particle image velocimetry (DPIV), while the velocities of the particles were obtained by image segmentation and processing of the dispersed phase from the DPIV images. To aide in visualizing the flow, the working fluid was an aqueous solution of sodium iodide with a refractive index matched to the particles. Comparing the velocity of the two phases, a particle velocity lag was observed at higher elevations, suggesting drag was the dominant fluid force on the particles, while observations of the particle motion indicated that collisions were important near the bed surface. Effects of different flow and initial conditions will be discussed. [Preview Abstract] |
Tuesday, November 20, 2012 8:52AM - 9:05AM |
M3.00005: Simulations of Multiphase Flow in a T-junction and Distributor Header Jeremy Horwitz, Purushotam Kumar, Pratap Vanka Multiphase flow is widely encountered in industrial applications including air conditioning and refrigeration systems. In this study, we simulate multiphase flow in complex micro-channels using two approaches: a multiphase Lattice Boltzmann Method (LBM) and a finite volume Volume of Fluid (VOF) method. In LBM, fluids are represented on a mesoscopic scale by particle distribution functions which evolve via a discretized Boltzmann equation. Macroscopic flow variables such as density and velocity are related to the moments of the distribution functions. In contrast, VOF calculates flow variables via three coupled equations: the continuity equation, the Navier-Stokes equation, and the volume-fraction transport equation which tracks the interface between disparate phases. An emphasis is placed on comparison of these schemes to determine their respective advantages in calculation of multiphase flow for these geometries. The principle geometries are a T-junction and multi-branch distributor header. We study bubble-laden flow and immiscible liquid-liquid flow and explore the effect of Reynolds number, buoyancy, and density ratio on the flow physics. Simulation results are compared with experiments. [Preview Abstract] |
Tuesday, November 20, 2012 9:05AM - 9:18AM |
M3.00006: Rotation of a spheroidal particle in Couette flow: effects of fluid and particle inertia Tomas Rosen, Fredrik Lundell, Minh Do-Quang, Cyrus K. Aidun Numerical simulations (Lattice Boltzmann simulations with External Boundary Force) of a single prolate spheroidal particle in a Couette flow have been performed, with the aim to study the transitions in particle rotation rate. The system is controlled by two dimensionless parameters, connected to fluid and particle inertia, respectively. Fluid inertia is controlled by the particle Reynolds number, \textit{Re}$_{p}$ and particle inertia is controlled by the Stokes number, \textit{St=$\alpha $Re}$_{p}$, where \textit{$\alpha $} is the density ratio between particle and fluid. Two transitions have been previously reported and are the main focus for this study. The first transition is that with increasing \textit{Re}$_{p}$, a light (buoyant) particle eventually ceases to rotate. The second is that a heavy particle, at a certain \textit{St}, undergoes a transition from a long period flipping motion to steady rotation with constant angular velocity. The results map out where particle or fluid inertia is more dominant. It was found that multiple solutions exist at constant \textit{Re}$_{p}$, where both periodic rotation and steady state can occur. This transition is determined by a critical density ratio,\textit{ $\alpha $}$_{c}$, for each \textit{Re}$_{p}$ and aspect ratio (length/width) of the particle. [Preview Abstract] |
Tuesday, November 20, 2012 9:18AM - 9:31AM |
M3.00007: Discrete Population Balance Multiphase Mixture Modeling of Fragmentation in Fully Developed Turbulent Duct Flow Aditya Jayanthi, John Peddieson A popular way to model particulate fragmentation is to divide the particle cloud into a finite number of size classes and allow transfer from larger to smaller size classes to simulate fragmentation. To use this approach effectively it is necessary to know the minimum number of size classes required for accurate predictions (size class convergence). In the present paper this question is addressed in the context of fragmentation in a fully developed turbulent duct flow using a multiphase mixture model of the particle cloud. Numerical solutions are obtained for a simple turbulence model and size class convergence is tested using two global measures of particle size distribution for several idealized fragmentation models. [Preview Abstract] |
Tuesday, November 20, 2012 9:31AM - 9:44AM |
M3.00008: On the effect of turbulence on bubbles in a horizontal channel flow Jerry Westerweel, Marc Harleman, Rene Delfos, Tom van Terwisga We present results on the concentration of small gas bubbles in water in a fully-developed horizontal turbulent channel flow. The bubble concentration reaches an equilibrium distribution that is characterized by the Rouse number. Results are obtained by both numerical simulations (DNS) and experiments (PIV) at comparable Reynolds numbers. The gas bubbles in the experiment have a Stokes number that is much smaller than unity, although they do not follow the fluid motion. The volume fraction is sufficiently low to assume one-way coupling. Dispite the low concentration and Stokes number, the bubbles appear to have a preferential concentration at the edge of a downward fluid motion away from the top channel wall. We present a simple model to explain the preferential concentration. For increasing Stokes numbers the rise velocity of individual bubbles in the turbulent channel flow appears to be only 40-50 per cent of the theoretical rise velocity for solid spheres (or gas bubbles in water containing impurities), while the gas bubble Reynolds number remains sufficiently small to assume only linear effects. This is in agreement with earlier reports on the sedimentation of solid particles in a turbulent flow. [Preview Abstract] |
Tuesday, November 20, 2012 9:44AM - 9:57AM |
M3.00009: Linear stability of double-diffusive two-fluid channel flow Kirti Sahu, Rama Govindarajan Double-diffusive density stratified systems are well studied and shown to display a rich variety of instability behaviour. However double diffusive systems where the inhomogeneities in solute concentration are manifested in terms of stratified viscosity rather than density have been studied far less, and not to our knowledge in high Reynolds number shear flows. In a simple geometry, namely the two-fluid channel flow of such a system, we find a new double-diffusive mode of instability. The instability becomes stronger as the ratio of diffusivities of the two scalars increases, even in a situation where the net Schmidt number decreases. The double-diffusive mode is destabilised when the layer of viscosity stratification overlaps with the critical layer of the perturbation. [Preview Abstract] |
Tuesday, November 20, 2012 9:57AM - 10:10AM |
M3.00010: Experimental investigation on rigid rod-like particles suspensions in archetypal flows by means of Particle Image Velocimetry Alessandro Capone, Alfredo Soldati, Giovanni Paolo Romano Results from an experimental investigation on rigid rod-like fiber particles suspensions in a turbulent pipe jet flow and a backward facing step flow using Particle Image Velocimetry are presented with a focus on turbulence modulation and fiber distribution and orientation. Specific post processing phase discrimination steps allowed simultaneous calculation of carrier and dispersed phase velocities. A turbulent pipe jet flow configuration was investigated in the jet near field region ($<$5D, where D represents the pipe diameter) within a Reynolds number range 8000-15000, based on D and jet bulk velocity. A turbulent backward facing step flow was analyzed up to 10H downstream of the step at a Reynolds number of 12000, based on step height H and maximum mean velocity. Both flows were tested at two fiber volume concentration C1=0.0001 and C2=0.0005. Results on turbulence modulation are presented as well as fiber concentration and distribution findings. High spatial resolution of backward facing step flow data and specific algorithms allowed fibers orientation detection and orientation distribution calculation. Results from fibers preferential orientation and distribution in the wall-normal direction at selected channel locations and along the flow direction are presented. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700